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I am trying to format a USB hard disk previously formatted with a Mac Mini on Windows, but it doesn't let me format it.

From the Microsoft Management Console, I was able to delete one partition, but I cannot format the hard disk, which is reported from Windows 7 to be a EFI disk (it doesn't report the file system, though).

How can I format it?

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up vote 3 down vote accepted

I have had this problem before. What happens is that the disk has a GUID Partition Table instead of being set up as a Master Boot Record. Windows seems to have serious problems getting things back to the way they should be. The easiest solution would be to hook it up to a Mac and use Disk Utility to repartition it, set it up as a Master Boot Record and format it as FAT. After that you can do whatever you want to it in Windows.

If you do not have access to a Mac to do this there is another solution that I know works for sure. If you have a Linux Live CD with GParted restart your computer and boot into it. If you do not have a Live CD you can download and burn the GParted Live CD. After you boot into the Linux environment you will be able to convert the drive to any filesystem and partition table you want.

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Thank you; this completely answer my question. :-) – kiamlaluno Aug 24 '10 at 3:54

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